\ tell 8th what the function expects:
"ZZ" "strdup" func: strdup
"VZ" "free" func: free
\ call the external funcs
"abc" dup     \ now we have two strings "abc" on the stack
strdup .s cr   \ after strdup, you'll have the new (but duplicate) string on the stack
\ the ".s" will show both strings and you can see they are different items on the stack
free   \ let the c library free the string